Preheat the oven to 180°C/350°F/gas 4. Line a 24cm square baking tin with greaseproof paper

Place chocolate into a large bowl, add the diced butter and place over a pan of simmering water, until melted, stirring regularly

Beat the eggs and castor sugar together till pale

Sift the cocoa powder and baking powder into a separate bowl, add the white chocolate chips

Mix the melted chocolate, with the eggs and sugar, then add the dry mix and white chocolate chips, beat everything together until you have a silky consistency

Pour the brownie mix into the baking tin, and place in the oven for around 15 minutes. You don't want to overcook them so, unlike cakes, you don't want a skewer to come out clean – the brownies should be slightly springy on the outside but still gooey in the middle.

Allow to cool in the tray, then carefully transfer to a large chopping board and cut into chunky squares